Rubber vulcanization accelerator



Patented Sept. 6, 1 932 UNITED STATES- LABORATORIES COMPANY, OF AKRON, OHIO, A CORPORATION OF OHIO RUBBER yULcAnIzArIoN nconnnaaron F0 Drawing.

This inventionis directed to the manufac ture of vulcanized rubber by a process wheremay be designated as organic xanthates. It.

is well known that the metallic salts of va- 152 rious xanthic acids have been prepared and 1 steam pressure per square inch) whereas,

proposed as accelerators" of vulcanization.

Such compounds have not met with generalsuccess as accelerators due primarily totheir instability and their tendency to cause scorching or prevulcanization during the milling of arubber stock. Metallic xanthates also fail for application as accelera tors in that they can be used only at'low vulcanization temperatures to pound:

1 is often necessary that such rapid accelerators shouldbe active at higher temperatures also.

The type of organic xanthates to which this invention refers are reaction products of a secondary amine with a metallic ethyl xanthate. One example of such a product is piperidine ethyl xanthate. This new compound has been found to have none of the drawbacks of metallic xanthates and has in addition the advantage of being water soluble which makes it valuable in the vulcanie zation of rubber in the form of latex or of dispersions.

Piperidine-ethyl-xanthate has been prepared by causing substantially equal mols of piperidine hydrochloride, sulphate or other suitable salt and a soluble salt of ethyl xanthic acid such as potassium or sodium ethyl xanthate to react in alcoholic solution. V

The alkali chloride was precipitated and filtered off, leaving an alcoholic solution of piperidine ethyl xanthate, which was obtained sufiiciently pure for use in the process set forth by evaporation of-the alcohol pref-,

Application filed'J'anuary 14,1928. Serial No. 246,919.

erably invacuuo when the piperidine ethyl xanthate was obtained as a crystalline solid.

PATENT oFFIca 3 .WINFIELID scorer, or nigpn wnsr VIRGINIA, ASSIGNOR TO marinas-Bria 'sEavroE 1 It'is not necessary to further purify this r'esidue after evaporating the alcoholic solution of piperidine ethyl xanthate since it contains no products detrimental to' rubber and can be prepared of substantially constant composition using uniformly pure materials for its preparation. This can be readily done since both piperidine hydrochloride and potassium or sodium xanthate can be prepared in constant purity. i The reaction products of other secondary amine hydrochlorides such as dieisoamylamine, dibutylamine and dibenzylamine and potassium ethyl xanthate have been prepared by proceeding in a like manner. 1

Other methods of preparing my preferred type of compoundmay, of course, be employed V V V In carrying out the invention in its-pref-erred form, a rubber mix comprising 100 parts of rubber, for example pale'crepe rubber, 5 parts zinc oxide, 0.25 parts-of ferric oxide, 2 parts of sulfur, is prepared in the well known manner and to this mix 0.30 parts of one of my new type of accelerators, for exam ple piperidine ethyl xanthate, is incorporated thereln.

' The following table shows the results of Modulus of elasticity in Time of Pressure at elongatlonsfif Elonga cure lbs. g tion at minutes steam a tea break It w ill be observed that better results are obtalnable at lower vulcanization temperatures which is in keeping more with'th-e be havior of the metallic xanthates than with other nitrogen containing ultra and semi ultra accelerators.

Piperidine ethyl Xanthate is a powerful accelerator for highly compounded stocks (as are used in the treads of pneumatic tires) cured at lower steam pressures. Such stocks possess a high modulus of elasticity and an excellent resistance to abrasion and tearing A typical tire tread stock was made up as follows:

* Parts 7 Carbon black 25.0 Cycline (mineral and cottonseed) 011-"; 1.0 Stearic acid n" 11.0

i Itican be seenfrom the tensile results that Mineral rubber Piperidine ethyl irarithater A sample of rubber prepared from this formula was fully vulcanized 'in'30 minutes at a temperature obtained from 30 pounds of steam pressure per square inch. The following table shows the results of the tensile tests obtained from sheets of rubbervulcanized for 30 and 90 minutes at the temperature obtained from 30 pounds of steam pressure per square inch. V

- Tensile Tensile F1011 a at 300% at 500% Tensile Steam 'elongaelongaat break break pressur tion tion a such a stock does not deteriorate appreciably on along o'vercure as the modulus figures show no decrease at the longer vperiod of cure. Such anaccelerator finds application in the vulcanization of thick articles, which due to the low heat conductivity of rubber, must necessarily be cured for'long periods of time.

A stock suitable for a tire cushion was prepared and tested, using one of my new type of compounds, j for example piperidine ethyl xanthate, as an accelerator. The, stock-consisted of 100 parts of rubber, for example pale crepe rubber, 15 parts of zinc oxide,

s2 parts sulfur and 0.2 parts of piperidin'e ethyl xanthate. After vulcanizing for 20 minutes at280 F., the cured product showed a load at 700% elongation of approximately;

1000 pounds per square inch and a tensile at breakof 2700 pounds per square inch; N

A hard rubber stock was prepared as follows Parts Smoked sheet 20.0 Lime 5.0 Zine oxide i 17.5 Mineral rubber 10.0 Sulfur 27.5 Piperidine ethyl xanthate; 0.5

inc, and dibenzylamine. products, (e.. g. .di-isoamylamine ethyl xan-. ithate, di-nbutylamine ethyl Xanthate and'di- A very hard rubber product was obtained by vulcanizing the above stock for two hours at 287 F. (40 pounds of steam pressure per square inch).

Other organic Xanthates have been prepared, according to the Jmaznner'I have outlined, from di-isoamylamine, di-n-butylam- These reaction benzylamine ethyl Xanthat'e') were incorporated into a rubber mix comprising 100 parts rubber, for example pale crepe rubber, 5

V 3 5 parts of zinc oxide,"3.5 parts of sulfur, and".

0.25 parts accelerator, and Vulcanized at 287 F. (40 pounds steam pres'sure'per square inch) for approximately 30 minutes whereby products exhibiting'the physical characteris-' tics as indicated in the following tablewere obtained. In'the following tableaccelerator N o. 1 means di-isoainylamine ethyl Xanthate;

accelerator N o. 2 "means 'di-n-b-u.tylamine ethyl Xan'thate accelerator No. 3 means di benzylamine ethyl xanthate. i

Cum Modulus of elasticity V V i minutes p /p1 t l Elongaat 40# 1011.50 Tensile tion at Accelerator steam' atbreak break i pressure 300% 500% 700% I 30 167 295 v 960 3070' [900 v 30 154 298 855 2735 30 134 233 424 1975 .945C

0 Although I have described several "exam; ples whereby my new'type of compounds may be prepared and used as rubber vulcanization accelerators, it is to. be understood-that this" invention is not limited to the specific examples set forth hereinfor illustrative purposes and that modifications of the invention may be resorted to. without departing from the spirit thereof orthe scope of the appended claims. i "What is claimed is;: 1. The process of preparing vulcanized rubber which comprises heating rubber and a vulcanizing agent in'the presenceof a. com? pound possessing the formula J A ,C H OCSSHR, V V 1 y where R is a completely hydrogenated cyclic amine.v V p 2. The process of preparing vulcanized rubber which comprises heating rubber and a vulcanizingagent in the presence of one of a group of compounds consisting-of piperi 4. "The vulcanized rubber product obtained by treating rubber and a vulcanizing agent in the presence of one of a group of compounds consisting of piperidine-ethyl- Xanthate, diiso-amyl amine-ethyl-xanthate, dibutylamine-ethyl-xanthate and dibenzylamine-ethyl-Xanthate.

5. The process of preparing vulcanized rubber which comprises heating rubber and a 'vulcanizing agent in the presence of a secondary amine salt of ethyl xanthic acid. 6. The process of preparing vulcanized rubber which comprises heating rubber and a vulcanizing agent in the presence of a secondlary aliphatic amine salt of ethyl Xanthic aci 7. The vulcanized rubber product obtained by heating rubber and a vulcanizing agent in the presence of a secondary amine salt of ethyl Xanthic acid.

8. The vulcanized rubber product obtained by heating rubber and a vulcanizing agent in the presence of a secondary aliphatic amine salt of ethyl xanthic acid.

In testimony whereof I hereunto aifix my signature.

WINFIELD SCOTT. 

